Means and method for reducing sparking in cathode ray tubes



3,536,527 MEANS AND METHOD FOR REDUCING SPARK- IING 1N CATHODE RAY TUBESLaszlo .lavorik and (Mo Landi, Chicago, and Robert A.

Mitchell, Berwyn, 111., assignors to National Video Corporation,Chicago, 111., a corporation of Illinois No Drawing. Filed Sept. 11,1967, Ser. No. 667,331 Int. Cl. 344d 1/02 US. Cl. 117-216 2 ClaimsABSTRACT OF THE DHSCLOSURE An anti-sparking coating for the interior ofa cathode ray tube which is applied over the usual electrically conductive carbonaceous coating, the supplemental coating consistingessentially of aluminum hydroxide and a soluble silicate.

SUMMARY OF THE INVENTION Cathode ray tubes conventionally have aninterior coating of an electrically conductive carbonaceous material.Commonly used for this purpose is a product known as Aquadag andcommonly referred to throughout the television industry as dag. Thecarbonaceous layer extends from near the edge of the funnel portion ofthe tube back into the gun portion and serves as a means for conductingelectric current to apply a potential of the order of 25 kv. to theelectron gun. Frequently during the life of such a tube, particles ofthe dag become detached from the coating and result in interior sparkingor arcing and consequently, a poor television picture. We have foundthat through the use of a supplemental coating, particularly onecompatible with the usual dag coating, this problem can be resolved. Wefind that a coating made up of aluminum hydroxide and a soluble silicateis particularly advantageous for this purpose. A specific example of thepractice of the invention is set forth below.

EXAMPLE For the purpose of preparing the anti-sparking coating material,we use one part by weight of deionized Water with one part by Weight ofpurified gelatinous aluminum hydroxide. This mixture is placed within aball mill using porcelain balls and milled for 24 hours at roomtemperature (6878 F.). Thereafter the suspension so achieved was mixedby taking 25 parts by volume of the aluminum hydroxide suspension andmixed with 75 parts by volume of potassium silicate solution (electronicgrade),

the potassium silicate solution having a specific gravity I of 1.26.This mixture was agitated for one hour and thereafter sprayed thoroughlyand evenly over the inner dag surface (which was previously baked to itsfinal condition) using airless spray apparatus. The supplemental coatingwas then baked dry in conventional fashion.

With the foregoing coating, We find that if there is any tendency of themultiple-coating to flake, it occurs in the aluminum oxide which Willnot cause sparking.

While in the foregoing specification a detailed description of anembodiment of the invention has been set down for the purpose ofillustration, many variations in the details herein given may be made bythose skilled in the art Without departing from the spirit and scope ofthe invention.

We claim:

1. In a cathode ray tube having an enlarged portion at one end providinga front viewing screen and a reduced portion at the other end housing anelectron gun, said tube having an interior electrically conductivecarbonaceous coating extending rearwardly from said screen, the improvedsupplemental coating interiorly of and on said carbonaceous coating andconsisting essentially of about 25 parts by volume of aluminum hydroxideand about parts by volume of potassium silicate.

2. In a method for suppressing sparking in cathode ray tubes having anelectrically conductive carbonaceous layer on the tube interiorextending rearwardly from the front viewing screen, the steps ofspraying over said layer an aqueous mixture consisting essentially ofabout 25 parts by volume of aluminum hydroxide and about 75 parts byvolume of potassium silicate, the said potassium silicate having aspecific gravity of about 1.26, and thereafter drying the sprayedmixture.

References Cited UNITED STATES PATENTS 2,223,924 12/1940 Stephan 313-64X 2,496,901 2/1950 Van Hoorn.

2,951,773 9/1960 Helle et al. 117-226 X 3,108,906 10/ 1963 Scharrer eta1 117-226 ALFRED L. LEAVITT, Primary Examiner C. K. WEIFFENBACH,Assistant Examiner US. Cl. X.R.

